Location of the extra testis:
(1) within the scrotum, proximal to the normal testis
(2) within the inguinal canal
(3) undescended (at the level of the L4 vertebral body)
(4) partially descended (anywhere between #2 and 3)
How the extra testis is identified:
(1) palpable nodule in the scrotum or inguinal canal
(2) tumor development
(3) incidental finding at surgery, autopsy or on an imaging study
(4) investigation of a vasectomy failure (hopefully this would be caught by failure of the sperm count to drop to 0 rather than by an unwanted pregnancy)
The extra testicle is usually removed to confirm the diagnosis and to make sure that it does not become a source for a germ cell tumor.
